Masonry arch bridges in the Italian railway engineering experience: state of condition, static reliability, seismic verification and retrofit strategies

Masonry arch bridges still represent a crucial element of the railway transportation network across Europe. Many of them are part of the historical heritage of the XIXth century, and are underdesigned for actual service conditions. Due to the intrinsic weakness of some structural components, to deterioration phenomena and to the updating of structural codes, masonry arched structures show often inadequate performance considering the static and seismic requirements of current codes. Reliable methods are thus required for the assessment of static and seismic reliability, and to prioritize retrofit interventions. Simplified procedures shall be used for large-scale planning: for this purpose the kinematic method, based on an adaptation of limit design for masonry structures, has proved to be a conceptually simple and robust procedure to verify the safety of masonry arches. Standard strategies should be finally proposed for the rehabilitation of arch bridges, taking into account to this end the original design and construction system and limiting to the minimum the required retrofit interventions.